Upgrade API server integration tests to use Fake Petstore spec #5419

[wing328]

Description

petstore-with-fake-endpoints-models-for-testing.yaml covers a lot more edge cases when comparing with the original one (petstore.yaml)

We'll need to to update petstore.yaml with petstore-with-fake-endpoints-models-for-testing.yaml so to ensure the edge cases are covered moving forward.

API servers using petstore-with-fake-endpoints-models-for-testing.yaml:

• C# (NancyFx, ASP.net Core)
• Elixir
• Erlang
• Go
• Haskell Servant
• JavaScript/NodeJS
• Java (MSF4J, Spring, Undertow, JAX-RS: CDI, CXF, Inflector, RestEasy)
• PHP (Lumen, Slim, Silex, Zend Expressive)
• Python Flask
• Ruby (Sinatra, Rails)
• Scala Finch
• Scala Scalatra

If anyone wants to work on the enhancement, please reply to let us know. Thank you!